feat(workflow): choose agent and model separately, ACP as the default runtime #64

Parent

#62

What to build

The authoring and config surface of ADR 0013 §2–§4. The ACP adapter (#63) becomes the default
runtime.

• agent?: "claude" | "opencode" next to model at every level: AgentCallOptions, the
  workflow agent defaults, schedule agent, and the run-request override.
• config.agent:
  • default (agent);
  • models: { claude?: string, opencode?: string };
  • hostSettings: { claude?: "ignore" | "include", opencode?: … }, with "ignore" as the
    default.
  • Keep config.agent.adapter as the injection point for replay and fakes.
• Resolution rule (ADR 0013 §2):
  • Agent: the most specific level that names one, else config.agent.default.
  • Model: the most specific level that names one, among the level that chose the agent and the
    levels more specific than it. Otherwise config.agent.models[agent].
  • Factory always sends a model. An unresolvable model fails the run at start with a clear
    message.
  • Unit-test the rule as a table.
• Remove DEFAULT_MODEL. Closes Add a config-level default agent model #40.
• Remove permissionMode from AgentCallOptions. Closes permissionMode is declared on the authoring surface and read by nobody #39.
• AgentStepStarted.agent, optional for old logs. Show the agent next to the model in run
  detail.
• factory init writes agent.default and agent.models (claude: "sonnet",
  opencode: "opencode/big-pickle").
• This repo's .factory/factory.config.ts gets the same.
• Daemon start runs feat(runtime): production ACP adapter for opencode and Claude Code #63's availability check for the configured agents and logs anything
  missing.

Acceptance

• bun run check green.
• A live factory start hello (or the spike workflow through the CLI path) on each agent picks
  the configured model.